The United States Capitol dome is the dome situated above the rotunda of the
United States Capitol. The dome is 288 feet in height and 96 feet in diameter. It was designed by Thomas U. Walter, the fourth Architect of the Capitol, and constructed between 1855 and 1866 at a cost of $1,047,291.
The dome is not stone, but rather cast iron carefully painted to appear to be made of the same stone as the main capitol building. It is actually two domes, one inside the other, and the total weight is 9.1 million pounds. The dome's cast iron frame was supplied and constructed by the iron foundry Janes, Fowler, Kirtland & Co. in the Bronx, New York. The dome marks the origin on street maps of Washington, D.C. A detailed look at the dome and its recent restoration can be found here.